The invention relates to a method and apparatus to produce sharp tips. Many techniques and recipes have been reported on the production of sharp tips. In particular, a recent article entitled "The art and science and other aspects of making sharp tips," J. Vac. Sci. and Technol., B 9 (2), Mar/Arp 1991 pp. 601-608, by Allan J. Melmed, summarizes most of them. Most of these techniques for tip production rely on empirical information collected through the years. The problem with all reported techniques is that they lack reliability. Unless each resulting tip is imaged by an electron microscope, there is no way to know whether the tip is sharp enough for an intended use. This is particularly crucial when the tip is to be used in a controlled environment such as vacuum or low temperature.
U.S. Pat. No. 4,375,396 teaches a basic electrochemical method for forming sharp tips on thin wires. It teaches monitoring the current and cutting the current when it reaches a certain level. It does not disclose moving the wire in and out of the electrolyte.
U.S. Pat. No. 4,935,865 teaches using a computer to control an electropolishing system but does not teach tip preparation.
U.S. Pat. No. 3,697,403 teaches monitoring and storing a control parameter such as voltage for use in a control system of an electrochemical grinding apparatus (see Summary of the Invention). The grinding apparatus employs a rotating type tool and does not relate to tip preparation.
U.S. Pat. No. 2,434,286 teaches an electromechanical method of forming a point at the end of a wire. However this method does not teach monitoring the current.
The Melmed paper discussed above discloses an electrochemical etching process including moving the tip out of the electrolyte while observing the etching process with a microscope. However, moving the tip in response to current monitoring is not taught.
Other references of general background interest are: "Platinum/Iridium tips with controlled geometry for scanning tunneling microscopy," by Inga Holl Musselman et al, J. Vac. Sci. Technol., A 8 (4), Jul/Aug 1990, pp. 3558, and "Preparation of STM tips for in-situ characterization of electrode surfaces," by Michael J. Heben et al, J. Microscopy, 152, 3, Dec 1988, pp. 651-661.